The use of carbon-based inks is known for the manufacture of carbon-based conductors, for example printed circuits and electrodes for sensors. In general, a carbon-based ink is an ink containing a carbon particulate such as graphite, amorphous carbon or a fullerene, suspended in a binder and a solvent. These inks are applied on a surface via a number of deposition techniques, including painting on with a brush, syringe application, and screen printing. The ink is allowed to dry and the resulting carbon-coated surface is subjected to a treatment at temperatures ranging from 50° C. to several hundred degrees Celsius. This high temperature treatment, or curing, is necessary to attain high conductivity in the resulting composite conductors.
The high temperatures needed for curing can limit the usefulness of carbon-based inks. The growing field of enzymatic electrochemical sensors is a case in point. In this type of sensor, a sensing electrode specific to a given analyte is made by linking or adsorbing a redox enzyme specific to the analyte of interest to a conductive surface. When the analyte is present in the sample being tested, electron transfer occurs and an electric signal proportional to the concentration of the analyte is thus generated. Examples include those described in U.S. Pat. Nos. 5,411,647; 5,476,776; 4,919,141; and 4,911,794. The sensor can also include an electron-transfer mediator that enhances the sensitivity of the system.
The enzyme typically is not incorporated in the ink, since it would denature and lose its activity during curing of the ink to increase the conductivity. This curing is necessary in order to optimize electron exchange between inks and enzymes. Thus, the sensor usually is manufactured by first applying and curing the carbon ink, and then the enzyme is adsorbed to the ink by immersion of the latter in a solution of the former.
One flexible and low cost way to manufacture these sensors would be by printing with a continuous ink-jet printer. However, the large particle size of the carbon particulate in the inks precludes their use in typical ink-jet printers. Thus, computers and peripherals typically cannot be used for flexible and low cost printing.